In situ combustion process utilizing waste heat



A ril 23, 1968 K. STRANGE 3,379,243

m srru comsuswxon BRocEss uwmzme WASTE HEAT Filed Dec. 10, I965 LLOYD K STRANGE INVENTOR BY 53M ATTORNEY 3,379,243 IN SITU CGMBUSTION FRGCESS UTILEZING WASTE HEAT Lloyd K. Strange, Grand Prairie, Tex, assignor to Mobil (Bil Qorporation, a corporation of New York Filed 10, 19-65, Ser. No. 513,139 Qlairns. (Cl. 166-11) ABTRACT IF THE DISCLGSURE This specification discloses:

Injecting water into a hot portion of a formation traversed by a combustion front to produce a flow of steam therefrom at certain temperature and pressure conditions. Heat energy is removed from the steam until a substantial part thereof is condensed to Water. This heat energy is employed to power mechan ms for moving fluids between the earths surface and a second portion of the formation in which in situ combustion is being undertaken. The water condensed from the steam may be used as feed water for conversion to steam by heat exchange with hot produced fluids. This resultant steam may also be employed for moving fluids between the earths surface and the portion of the formation in which in situ combustion is being undertaken.

This process relates to the recovery of hydrocarbons from a subterranean formation, and more particularly, it relates to the recovery of such hydrocarbons by an improved in situ combustion procedure.

The recovery of hydrocarbons may be effected from a subterranean formation by various in situ combustion procedures. In such procedures, a combustion front is moved etween input and output well means through the subterr nean formation by the passage therethrough of a combustion-supporting gas from input to output well means. As a result of the fronts passage, with its elevated temperatures, hydrocarbons are thermally stimulated to flow through the formation and to be produced from output well means, The portion of the formation traversed by the combustion front remains at elevated temperatures. The elevated temperatures in such portion of the formation result from the substantially complete combustion of resident carbonaceous materials and may reach a magnitude, for example, of about 1000 F. As is apparent, large quantities of energy are expended in an in situ combustion process for the compression and movement of a combustion-supporting gas through the subterranean formation and also for the production and subsequent recovery of the desired hydrocarbons. It is the purpose of the present invention to employ the heat energy remaining within that portion of the formation traversed by a combustion front and which portion remains at elevated temperature to assist in carrying out the in situ combustion procedure in unburned portions of the formation.

It is therefore an object of the present invention to provide an improved in situ combustion process for the recovery of hydrocarbons from a subterranean formation wherein the heat energy remaining in that portion of the formation traversed by a combustion front is employed for carrying out the in situ combustion procedure in further portions of the formation. Other objects of the in vention will become apparent on consideration of the ac companying description.

The present invention in its broadest aspect comprises the injection of water into a portion of the formation, which remains at elevated temperatures after being traversed by a combustion front, so as to produce a flow of steam therefrom at a temperature above the condensation temperature of water at the pressure existing in the flow- States Patent 0 ing steam through suitable Well means, Thereafter, heat energy is removed from the steam until a substantial part thereof is condensed to water and the heat energy removed from the steam is employed for moving fluids between the earths surface and the second portion of the formation in which in situ combustion is being undertaken. ()ther aspects of the present invention include employing the water condensed from the steam as feed water for reconversion to steam with the resulting steam at least in part employed for moving fluids between the earths surface and another portion of the formation in which in situ combustion is undertaken.

The present invention will be now described in reference to the attached drawings, wherein: FIGURE 1 is a vertical section of a subterranean formation provided with suitable apparatus by which hydrocarbons are recovered in accordance with this improved in situ combustion process with a combustion front being shown during its initial stages of movement through the formation between well means; FIGURE 2 illustrates the structure of FIGURE 1 but with the combustion front having nearly traversed the entire formation between the well means; and FIGURE 3 illustrates the structures of FIGURES 1 and 2 after the formation between the well means is completely traversed by the combustion front.

In FIGURE 1, a subterranean formation 11 from which hydrocarbons can be freed by an in situ combustion process is shown residing below the earths surface 12. Usually, the formation 11 resides below an overburden 13 of earthen materials, and in many instances, there may be additional superimposed strata 14 of a rock material relatively free of carbonaceous material. The formation 11 usually rests upon a substrata 16 which, like the strata 14, may be free of any recoverable carbonaceous material, A plurality of well means, extending vertically into the earth, provide for fluid communication between the earths surface 12 and the formation 11. These well means may include one or more input wells 17 and one or more output wells 13, which may be provided in any suitable manner. The wells 17 and is are provided with casings I9 and 21, respectively, extending downwardly into the formation 11 with. fluid communication at their lower extremities directly to the formation 11. Such fluid communication may be by terminating the casings 19 and 21 short of the lower extremities of the wells 17 and 18 in the formation 11, by perforations therethrough, or by other suitable modes. At the top of the casings I9 and 2.: are carried wellheads 22 and 23, respectively, through which fluid conduits 24 and 26, respectively, extend downwardly to the lower extremities of wells 17 and 18. The fluid conduits 24 and 26 convey fluids between the earths surface 12 and the formation 11. Generally, the casings 19 and 21 are secured in fluid-tight engagement with the overburden 13 and the strata 14, preferably by cementing. The arrangement in FIGURES 2 and 3 of the structures including the formation 11 and Well means may be considered to be identical to that of FIGURE 1, and for purposes of description like reference numerals are used. However, it will be apparent that other arrangements for these structures may be used with equal facility.

In situ combustion processes now may be carried out in the formation 11 with the described structural arrangements. For this purpose, the formation 11 adjacent the well 17 is heated sufliciently for igniting the carbonaceous material contained therein. Such igniting means may be of any suitable form, such as electric igniters or other types of heaters. With the formation lit at ignition temperatures, a combustion-supporting gas is passed into the conduit 2% under suitable flow conditions to traverse the formation 11 and be produced from the conduit 26 in the well 18. The combustion-supporting gas may include any oxidant for sustaining combustion, usually air. However, it may also be a combination of oxygencontaining materials enriched or diluted with inert or combustion-supporting gases, as is well known to those skilled in the art. The combustion-supporting gas traversing the formation 11 produces a combustion front 27 which moves between the wells 17 and 18. Although the description herein is directed toward a direct movement combustion front 27, the combustion front may be moved inversely to the flow of the combustion supporting gas to roduce the results of this invention with equal facility. The heat generated by the combustion front 27 moving through the formation 11 thermally releases the hydrocarbons from the formation 11. These hydrocarbons are carried concurrently with the injected combustion-supporting and residual-combustion gases into the well 18 and are produced from the conduit 26. The produced fluids from the conduit 26 are passed to any suitable utilization, such as to a separator in which the hydrocarbons are recovered from water and inert fluids.

Referring now to FIGURE 2, it will be seen that after some period of time of injecting the combustion-supporting gas, the combustion front 27 has advanced adjacent to the output well 18, over a substantial portion of the formation 11 which is freed of combustible carbonaceous material. At the time the combustion front 27 first appears at the output well 18, the produced fluids from the conduit 26 will become in part heated to elevated temperatures. The heat energy contained in these produced fluids will be employed, as described hereinafter, for further purposes of this invention.

Referring now to FIGURE 3, it will be seen that eventually the combustion front 27 will substantially and completely sweep that portion of the formation 11 residing between the wells 17 and 18. The combustion front 27 may then move beyond the well 18 in the formation 11. Alternatively, the combustion front 27, at this time, may be extinguished. If desired, other portions of the formation f1 may be subject to traverse of the combustion front 27 as was shown and described relative to FIGURES l, 2 and 3.

In FIGURE 3, the formation 11 traversed by the combustion front 27 is heated to elevated temperatures of about 1000 F. At this time, water is passed through the conduit 24 into the well -17 under suitable pressure to enter the burned out portion of the formation 11 residing between the wells 17 and 18. The water is injected into the formation 11 at a rate sutflcient to produce from the well 18 a flow of steam at a temperature at or above the condensation temperature of water at the pressure existing in the flowing steam. It will be seen that the raw water introduced from the well 17 into the hot formation 11 will be in situ converted to steam, and that the steam produced from the well 18 will be substantially free of entrained inorganic materials which remain in the formation 11. The raw water can be from any source which is available and includes brine-loaded oil field water, sea water, and the like. Thus, raw water is converted into steam substantially free of inorganic materials. This steam is utilized for further purposes in the present process.

The formation 11 is filled by the raw water as it cools during the generation of steam. This is of particular advantage in that no re-invasion of the water-filled formation 11 by hydrocarbons produced from adjacent portions of the formation can occur.

The steam produced from the well 18 carries a considerable amount of heat energy recovered from the formation 11. For example, one acre-foot of the burned out formation 11, as for example in a heavy oil sand, may reside after being burned at a temperature of about 1000 F. The heat content of the formation 11 under these conditions is approximately 800 million B.t.u. A portion of the formation 11 adjacent the input well 17 may be cooled by the injected fluids moving the combustion front 27 to the well 18. However, the estimated heat lost in this cool region by the input well 17 will be approximately only 250 million B.t.u. Thus, the heat energy within the burned out formation available for conversion to steam is about 550 million B.t.u. It is estimated that the heat energy required to drive compressors to inject sufficient combustion-supporting gas to move a combustion front through such area of the formation 11 is about 1000 million B.t.u. Thus, the heat energy contained in the burned out formation 11 between the wells 17 and 18 can provide over half the amount of heat energy required to inject the combustion supporting gas moving a combustion front through a like area in the formation 11.

A suitable system to utilize the heat energy of the steam produced from tle formation 11 through the conduit 26 is shown in FIGURE 3. Usually, the steam from the conduit 26 will be passed to a separator 31 in which hydrocarbon and water portions may be removed from outlets 32 and 33, respectively, and the remaining steam leaves through overhead line 34. Since the formation 11 was substantially freed of carbonaceous material, the steam in line 34 will be largely free of hydrocarbons. The steam in line 34 is passed through a steam engine means, which may be turbine 35, wherein heat energy is removed from the steam by conversion to mechanical energy until a substantial part is condensed to water which is removed in the line 37. The mechanical energy output of the turbine 36 is applied to operate the pumping means, such as compressor 38, which is employed for injecting the combustion-supporting gas into the input well 17. At times when the flow of steam may be insufficient to operate the turbine 36 at the desired capacity, the steam in line 34 can be supplemented by steam from a suitable steam generator 39. The steam generator 39, of any suitable form capable of converting water into steam, provides steam in an out put steam line 41 which is combinable with steam in the line 34- for operating the turbine 36. Valves 43 and 44 may be interposed into the respective steam lines 34 and 41 for selectively controlling the source and amounts of steam from the separator 31 and the steam generator 39 passing to the turbine 36. The steam generator 39 may be operated from any source of combustible fuel supplied to fuel inlet 45 in the usual fashion. After combustion of the fuel, the exhaust vapors pass from the steam generator 39 through the stack 47.

The steam generator 39 requires a source of suitable feed water for its operation which generally requires softening of raw or naturally occurring water. Raw water is passed through a treater 48, such as a sodium zeolite bed, wherein scale-forming constituents are converted to a more soluble form. The treated water from the treater 48 is collected in tank 4*) until it is to be supplied to the steam generator 39. The feed water from the tank 49 passes through a heat exchanger 51 and thence to feed water inlet 56 of the steam generator 39 by suitable pumping means (not shown). The feed water in the heat exchanger 51 derives heat from the produced fluids obtained from the well 18 (in FIGURE 2) when such fluids are heated sufficiently that their heat content is usable. From the heat exchanger 51 these produced fluids may be passed to a separator 52 and the contained gases and liquids may be removed through outlets 53, 54, and 55. A bypass line 56 is provided about the heat exchanger 51 when it is desired not to employ the heat within the produced fluids from the well 18 for preheating the feed water to the steam generator 39. Valves 5'7 and 58 are provided for this function. The condensate in line 37 from the turbine 36 is combined as needed with the feed water from the tank 49. It will be apparent that a substantial part of the water for the steam generator 39 will come from the turbine 36. This is of great advantage in that the costs for treating the water to a suitable degree for use in the same generator 39 are greatly reduced by the amount of steam produced from the well l8. Further, the costs of water are reduced in that brine water may be injected into the well 17 with the production of solid and salt-free steam from the well 18 being obtained. Also, the necessity of disposing of the scale-forming inorganic materials ordinarily a problem with a surface treater 48 is avoided.

It will be apparent that the compressor 38 may be employed for injecting combustion-supporting gas into various of the combustion fronts employed in the formation 11 and at any stage therein whether such combustion fronts are operated conjunctively or serially, or a combination of both.

It will be apparent that Where it is desired to do so, the mechanical output of the turbine 36 may be employed for driving other types of pumping means than the compressor 38, such as pumps for moving the produced fluids from the well 18 to suitable storage. Also, the heat energy of the stream from the well 18 (in FIGURE 2) may be employed in breaking emulsions and otherwise treating the produced fluids, or for other purposes as desired.

From the foregoing description it will be apparent that there has been provided a process suited for obtaining all the objects stated for the present invention. It will be readily appreciated from the foregoing description that herein is fully disclosed a process also adapted for Ohtaining recovery of hydrocarbons from formations with the utilization of waste heat from in situ combustion procedures.

It will be understood that certain features of the present procedure are of utility and may be employed without reference to other features and combinations. This is contemplated by and within the scope of the appended claims.

As many embodiments as possible may be made of the invention without departing from the scope thereof. It is to be understood that all matter herein set forth is to be interpreted as illustrative and not limitative of this invention.

What is claimed is:

1. In an in situ combustion process for the recovery of hydrocarbons from a subterranean formation wherein a combustion front is moved between input and output well means through the formation by the passage therethrough of a combustion-supporting gas from input to output well means, and with said hydrocarbons produced from said output well means, the improvement comprising:

(a) passing a combustion front through a first portion of the formation between input and output well means, and producing and recovering hydrocarbons from the output well means so as to leave said first portion at elevated temperatures resulting from substantially complete combustion of resident carbonaceous matter,

(b) moving a second combustion front through a second portion of the formation by passing a combustion-supporting gas between input and output well means with hydrocarbons at least in part heated to elevated temperatures being produced from the output well means,

(c) injecting water into the first portion of the formation at a rate suflicient to produce a flow of steam from one of said well means at a temperature above the condensation temperature of water at the pressure existing in said flowing steam,

(c1 removing heat energy from said steam until a substantlal part thereof is condensed to water, and

(e) employing said heat energy for moving fluids between the earths surface and the second portion of the formation in which in situ combustion is being undertaken.

2. The method of claim 1 wherein at least a part of said condensed water from Step d is reconverted to steam in surface disposed steam generating means with the steam at least in part employed for moving fluids between the earths surface and the second portion of the formation in which in situ combustion is undertaken.

3. The method of claim 1 wherein steam produced in Step c is converted in Step d to mechanical power adapted for operating pumping means to move fluids in Step e between the earths surface and the second portion of the formation in which in situ combustion is undertaken.

4. The method of claim 1 wherein Step e heat energy is employed for converting the condensed water from Step (1 into steam, and at least a part of the generated steam is employed for moving fluids between the earths surface and the second portion of the formation in which in situ combustion is being undertaken.

5. The method of claim 4 wherein the produced hydrocarbons in Step b, when in a heated condition, are heat exchanged with the water being converted to steam.

References Cited UNITED STATES PATENTS 2,497,868 2/1950 Dalin 166-39 X 2,823,752 2/1958 Walter 166-11 2,839,141 6/1958 Walter 166-11 3,113,620 12/1963 Hemminger 166-11 3,150,716 9/1964 Strelzotf et a1. 166-11 3,193,009 7/1965 Wallace et al. 166-11 3,294,167 12/1966 Vogel 166-11 STEPHEN J. NOVOSAD, Primary Examiner. 

